Electronically scanned antenna arrays are well known, as suggested in chapter 11 of Radar Handbook (McGraw-Hill, 1970; M. I. Skolnik, Ed.). Such kinds of antennae are frequently used in radar systems. The antennae used particularly comprise arrays of individual radiating elements, which are electronically phase scanned.
The manufacture and assembly of such an antenna nonetheless remains a difficult task. Substantial errors in the phase of individual elements of the array are created even if manufacture is conducted within acceptable manufacturing tolerances. These errors may accumulate, resulting in overall antenna aperture phase errors.
Accordingly, at first manufacture and assembly, an initial antenna aperture phase measurement is conducted and suitable corrections and adjustments in the manufactured antenna are introduced. The initial measurement consists of accurately measuring the radiated phase of each antenna array element by near-field probing. Then phase correction for the relative errors in phase between respective elements is made, by introducing adjustment factors into the memory of the computer directing the electronic beam steering phasers.
In particular, the radiated phase and amplitude of every element of the array are individually examined to determine deviation from design parameters. These errors can be mechanically or electrically eliminated by making suitable adjustments.
To produce a low sidelobe antenna radiation pattern, laborious precision measurements and adjustments are made in a test laboratory. These adjustments require physical access to the antenna radiating surface in many cases.
However, even after initial adjustment, phase deviations continue to affect performance as a result of environmental factors, component failure and component replacement. In other words, the tight phase tolerances of the antenna aperture degrade, creating phase errors, largely caused by aging, deformation, and component replacement activities. The necessary phase corrections are typically conducted by returning the antenna to an antenna test site on calibration laboratory or phase realignment. In lieu of such involved procedures, it is considered beneficial to make phase corrections, while the antenna is operating on-line during flight operations, for example.
No technique accomplishing this objective is known at this time, which is effective in precisely the same fashion as the invention herein sets forth. However, one phase/amplitude aperture measuring technique for an electronically phased array is known which is relevant as background to the invention presented herein. This technique does not require access to the antenna radiating surface. This technique is effectively described by Mr. Dan Davis in the February 1978 issue of the Microwave Journal. Mr. Davis' method requires that the antenna be installed on a precision rotating positioner while receiving a far-field radiated signal. Antenna phase and amplitude values received at the antenna input port are then accurately measured for prescribed angular positions of the rotating antenna positioner. One position is employed for each radiating element in the antenna array.
Subsequent computation by means of a relatively simple algorithm generates radiated phase and amplitude values of every element of the antenna array. Addition of the negated values of the measured degrees of phase and of the amount of amplitude deviation to each element excitation voltage results in an optimized, minimum-sidelobe antenna.
However, instead of conducting such measurements in a laboratory or as described in the Davis article, it is desirable to perform them right in the aircraft under operational conditions.